Showing papers on "Methyl vinyl ketone published in 2020"
TL;DR: This study reports the first experimental evidence of this novel decay pathway, which is predicted to be the dominant atmospheric sink for specific conformational forms of MVK-oxide and MACR-oxide with the vinyl substituent adjacent to the terminal O atom.
Abstract: Ozonolysis of isoprene, one of the most abundant volatile organic compounds emitted into the Earth’s atmosphere, generates two four-carbon unsaturated Criegee intermediates, methyl vinyl ketone oxi...
29 citations
TL;DR: In this article, the performance and mechanism for the selective catalytic oxidation of isopropanol to acetone were investigated using α-Fe2O3 nanosheet supported 0.38, 0.81, and 1.36 wt% Au nanocatalysts.
Abstract: We prepare α-Fe2O3 nanosheet supported 0.38, 0.81, and 1.36 wt% Au (average particle size = 4.0 nm) nanocatalysts, and investigate their performance and mechanism for the selective catalytic oxidation of isopropanol to acetone. In the presence of 1.2 vol% isopropanol and 40 vol% O2, 1.36 wt% Au/α-Fe2O3 exhibits excellent catalytic performance, due to its moderate acidic sites and better redox properties, with acetone selectivity and yield being as high as 99% and 95% at 220 oC, respectively. In addition to acetone, little propylene, acetic acid, acetaldehyde, methyl vinyl ketone, 2-butanone, isopropyl ether, isopropyl acetate, 3-penten-2-one, isopropyl acrylate, isopropyl propionate, and 2, 4-dimethylfuran are detected. The possible reaction mechanism is proposed for the selective catalytic oxidation of isopropanol to acetone over the present catalysts. We believe the present selective catalytic oxidation method, rather than the traditional complete catalytic oxidation method, provides an alternative and economic method for VOCs emissions control.
27 citations
TL;DR: This work provides the first experimental evidence that the simplest Diels–Alder reactions are not endo-selective, and trends in behaviour are traced to steric and electronic effects in Diels-Alder transition structures, giving new insights into these fundamental processes.
Abstract: There is a widespread perception that the high level of endo selectivity witnessed in many Diels–Alder reactions is an intrinsic feature of the transformation. In contrast to expectations based upon this existing belief, the first experimental Diels–Alder reactions of a novel, deuterium-labeled 1,3-butadiene with commonly used mono-substituted alkenic dienophiles (acrolein, methyl vinyl ketone, acrylic acid, methyl acrylate, acrylamide and acrylonitrile) reveal kinetic endo : exo ratios close to 1 : 1. Maleonitrile, butenolide, α-methylene γ-butyrolactone, and N-methylmaleimide behave differently, as does methyl vinyl ketone under Lewis acid catalysis. CBS-QB3 calculations incorporating solvent and temperature parameters give endo : exo product ratios that are in near quantitative agreement with these and earlier experimental findings. This work challenges the preconception of innate endo-selectivity by providing the first experimental evidence that the simplest Diels–Alder reactions are not endo-selective. Trends in behaviour are traced to steric and electronic effects in Diels–Alder transition structures, giving new insights into these fundamental processes.
21 citations
TL;DR: In this article, the unimolecular decay rate coefficient of syn-MVKO was measured to be kuni = 70 ± 15 s-1 (1σ uncertainty) at 298 K with negligible pressure dependence.
Abstract: Isoprene is the most abundant unsaturated hydrocarbon in the atmosphere. Ozonolysis of isoprene produces methyl vinyl ketone oxide (MVKO), which may react with atmospheric SO2, formic acid, and other important species at substantial levels. In this study, we utilized ultraviolet absorption to monitor the unimolecular decay kinetics of syn-MVKO in real time at 278-319 K and 100-503 Torr. After removing the contributions of radical reactions and wall loss, the unimolecular decay rate coefficient of syn-MVKO was measured to be kuni = 70 ± 15 s-1 (1σ uncertainty) at 298 K with negligible pressure dependence. In addition, kuni increases from ca. 30 s-1 at 278 K to ca. 175 s-1 at 319 K with an effective Arrhenius activation energy of 8.3 ± 2.5 kcal mol-1, kuni(T) = (9.3 × 107)exp(-4200/T) s-1. Our results indicate that unimolecular decay is the major sink of MVKO in the troposphere. The data would improve the estimation for the steady-state concentrations of MVKO and thus its oxidizing ability.
12 citations
TL;DR: The observation of higher levels of HMPMA-3 than the other two mercapturic acids suggests a previously unrecognized potential significance of methyl vinyl ketone as a toxicant in smokers and non-smokers.
Abstract: Using improved HPLC analysis conditions, we report the separation of three isomers of mercapturic acid conjugates previously assigned in the literature only to 3-hydroxy-1-methylpropylmercapturic acid (HMPMA-1), a human urinary metabolite of crotonaldehyde. The new conditions, employing a biphenyl column cooled to 5 °C and eluted with a gradient of formic acid, acetonitrile, and methanol, allow the analysis of human urinary mercapturic acids derived not only from crotonaldehyde but also from its isomers methacrolein (3-hydroxy-2-methylpropyl mercapturic acid, HMPMA-2) and methyl vinyl ketone (3-hydroxy-3-methylpropyl mercapturic acid, HMPMA-3). The mercapturic acids were detected and quantified by LC-ESI-MS/MS using the corresponding stable isotope labeled mercapturic acids as internal standards. The analysis was validated for accuracy and precision and applied to urine samples collected from cigarette smokers and nonsmokers. Smokers had significantly higher levels of all three mercapturic acids than did nonsmokers. The results demonstrated that HMPMA-3 from methyl vinyl ketone comprised the major portion of the peaks previously ascribed in multiple studies to HMPMA-1. HMPMA-1 had concentrations intermediate between those of HMPMA-2 and HMPMA-3 in both smokers and nonsmokers. This study reports the first quantitation of HMPMA-2 and HMPMA-3 in human urine. The observation of higher levels of HMPMA-3 than in the other two mercapturic acids suggests a previously unrecognized potential significance of methyl vinyl ketone as a toxicant in smokers and nonsmokers.
10 citations
TL;DR: Direct observation of HPBD generated by formic acid catalyzed isomerization of MVK-oxide under thermal conditions is reported using multiplexed photoionization mass spectrometry.
Abstract: Isoprene is the most abundant non-methane hydrocarbon emitted into the Earth's atmosphere. Ozonolysis is an important atmospheric sink for isoprene, which generates reactive carbonyl oxide species (R1R2C[double bond, length as m-dash]O+O-) known as Criegee intermediates. This study focuses on characterizing the catalyzed isomerization and adduct formation pathways for the reaction between formic acid and methyl vinyl ketone oxide (MVK-oxide), a four-carbon unsaturated Criegee intermediate generated from isoprene ozonolysis. syn-MVK-oxide undergoes intramolecular 1,4 H-atom transfer to form a substituted vinyl hydroperoxide intermediate, 2-hydroperoxybuta-1,3-diene (HPBD), which subsequently decomposes to hydroxyl and vinoxylic radical products. Here, we report direct observation of HPBD generated by formic acid catalyzed isomerization of MVK-oxide under thermal conditions (298 K, 10 torr) using multiplexed photoionization mass spectrometry. The acid catalyzed isomerization of MVK-oxide proceeds by a double hydrogen-bonded interaction followed by a concerted H-atom transfer via submerged barriers to produce HPBD and regenerate formic acid. The analogous isomerization pathway catalyzed with deuterated formic acid (D2-formic acid) enables migration of a D atom to yield partially deuterated HPBD (DPBD), which is identified by its distinct mass (m/z 87) and photoionization threshold. In addition, bimolecular reaction of MVK-oxide with D2-formic acid forms a functionalized hydroperoxide adduct, which is the dominant product channel, and is compared to a previous bimolecular reaction study with normal formic acid. Complementary high-level theoretical calculations are performed to further investigate the reaction pathways and kinetics.
10 citations
TL;DR: The experiments indicate that NO3 radical reactions with all the studied unsaturated VOCs proceed through addition to the olefinic bond, however, it indicates that the introduction of a carbonyl group into unsaturatedVOCs can deactivate the neighboring oleFinic bond towards reaction with the NO3radical, which is to be expected.
Abstract: Rate coefficients for the reaction of NO3 radicals with 6 unsaturated volatile organic compounds (VOCs) in a 7300 L simulation chamber at ambient temperature and pressure have been determined by the relative rate method. The resulting rate coefficients were determined for isoprene, 2-carene, 3-carene, methyl vinyl ketone (MVK), methacrolein (MACR) and crotonaldehyde (CA), as (6.6 ± 0.8) × 10−13, (1.8 ± 0.6) × 10−11, (8.7 ± 0.5) × 10−12, (1.24 ± 1.04) × 10−16, (3.3 ± 0.9) × 10−15 and (5.7 ± 1.2) × 10−15 cm3/(molecule•sec), respectively. The experiments indicate that NO3 radical reactions with all the studied unsaturated VOCs proceed through addition to the olefinic bond, however, it indicates that the introduction of a carbonyl group into unsaturated VOCs can deactivate the neighboring olefinic bond towards reaction with the NO3 radical, which is to be expected since the presence of these electron-withdrawing substituents will reduce the electron density in the π orbitals of the alkenes, and will therefore reduce the rate coefficient of these electrophilic addition reactions. In addition, we investigated the product formation from the reactions of 2-carene and 3-carene with the NO3 radical. Qualitative identification of an epoxide (C10H16OH+), caronaldehyde (C10H16O2H+) and nitrooxy-ketone (C10H16O4NH+) was achieved using a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and a reaction mechanism is proposed.
9 citations
TL;DR: The experimental data are consistent with a kinetic model that the reaction goes through an adduct of CH3(C2H3)CIOO, similar to the cases of H/alkyl substituted Criegee intermediates, however, this vinyl adduct is less stable and decomposes to MVKO + I at a time scale of 10-3 s (faster at higher temperature), consistent with the results of quantum chemistry calculations.
Abstract: Isoprene is the most abundant alkene in the atmosphere. Ozonolysis of isoprene produces three very reactive carbonyl oxides (Criegee intermediates), including formaldehyde oxide, methyl vinyl ketone oxide (MVKO, CH3(C2H3)COO), and methacrolein oxide. The latter two Criegee intermediates are resonance-stabilized due to the vinyl group. Recently, the electronic spectrum of thermalized MVKO has been reported [Caravan, et al., Proc. Natl. Acad. Sci. U. S. A., 2020, 117, 9733]. In this work, we utilized this strong UV/visible absorption to investigate the reaction kinetics of MVKO with SO2 under a wide pressure range of 4 to 700 Torr. We followed a new method [Barber, et al., J. Am. Chem. Soc., 2018, 140, 10866], in which MVKO is produced through the reaction of a resonance-stabilized iodoalkene radical with O2. The experimental data are consistent with a kinetic model that the reaction goes through an adduct of CH3(C2H3)CIOO, similar to the cases of H/alkyl substituted Criegee intermediates. However, different from the H/alkyl adducts, which are stable over the time scales of typical kinetic experiments, this vinyl adduct CH3(C2H3)CIOO is less stable and decomposes to MVKO + I at a time scale of 10-3 s (faster at higher temperature), consistent with the results of quantum chemistry calculations and the fact that the resonance stabilization is disrupted at the adduct structure. The adduct decomposition is the major pathway that forms MVKO for pressures higher than 50 Torr. In addition, temperature dependence has been investigated for 278-319 K. The experimental activation energy of the adduct decomposition was measured to be 12.7 ± 0.3 kcal mol-1, consistent with the calculated dissociation energy of the adduct to MVKO + I (14 kcal mol-1). Furthermore, the temperature dependent rate coefficient of MVKO + SO2 reaction has been measured to be kSO2 = (4.0 ± 0.6) × 10-11 cm3 s-1 at 4-700 Torr and 298 K with a negative activation energy of -3.7 ± 0.4 kcal mol-1.
9 citations
TL;DR: The CAHOF material functioned as a new type of catalytically active Brønsted acid in a series of reactions, including the ring opening of epoxides by water and alcohols.
Abstract: The acid-base neutralization reaction of commercially available disodium 2,6-naphthalenedisulfonate (NDS, 2 equivalents) and the tetrahydrochloride salt of tetrakis(4-aminophenyl)methane (TAPM, 1 equivalent) in water gave a novel three-dimensional charge-assisted hydrogen-bonded framework (CAHOF, F-1). The framework F-1 was characterized by X-ray diffraction, TGA, elemental analysis, and 1H NMR spectroscopy. The framework was supported by hydrogen bonds between the sulfonate anions and the ammonium cations of NDS and protonated TAPM moieties, respectively. The CAHOF material functioned as a new type of catalytically active Bronsted acid in a series of reactions, including the ring opening of epoxides by water and alcohols. A Diels-Alder reaction between cyclopentadiene and methyl vinyl ketone was also catalyzed by F-1 in heptane. Depending on the polarity of the solvent mixture, the CAHOF F-1 could function as a purely heterogeneous catalyst or partly dissociate, providing some dissolved F-1 as the real catalyst. In all cases, the catalyst could easily be recovered and recycled.
8 citations
TL;DR: It is revealed that the rate determining step in the Friedel-Crafts transformations can shift from carbon-carbon bond formation to proton transfer to the catalyst's conjugate base, which leads to an inverted parabolic reaction rate profile and slower reactions with more acidic catalysts in some cases.
Abstract: Charge-enhanced Bronsted acid organocatalysts with electron-withdrawing substituents were synthesized, and their relative acidities were characterized by computations, 1:1 binding equilibrium constants (K1:1) with a UV-vis active sensor, 31P NMR shifts upon coordination with triethylphosphine oxide, and in one case by infrared spectroscopy. Pseudo-first-order rate constants were determined for the Friedel-Crafts alkylations of N-methylindole with trans-β-nitrostyrene and 2,2,2-trifluoroacetophenone and the Diels-Alder reaction of cyclopentadiene with methyl vinyl ketone. These results along with kinetic isotope effect determinations revealed that the rate-determining step in the Friedel-Crafts transformations can shift from carbon-carbon bond formation to proton transfer to the catalyst's conjugate base. This leads to an inverted parabolic reaction rate profile and slower reactions with more acidic catalysts in some cases. Electron-withdrawing groups placed on the N-vinyl and N-aryl substituents of hydroxypyridinium ion salts lead to enhanced acidities, more acidic catalysts than trifluoroacetic acid, and a linear correlation between the logarithms of the Diels-Alder rate constants and measured K1:1 values.
8 citations
TL;DR: Pure rotational transitions of methyl vinyl ketone oxide, or so called methyl-vinyl Criegee intermediate, were observed by Fourier-transform microwave spectroscopy, and reasonably agrees with a theoretical value of 680 cm-1 determined with CCSD(T)/cc-pVTZ.
Abstract: Pure rotational transitions of methyl vinyl ketone oxide, or the so called methyl-vinyl Criegee intermediate, were observed by Fourier-transform microwave spectroscopy. Among the four possible conformers of this species, predicted by theory within an energy window of 3 kcal/mol, only the lowest-energy conformer, the syn-trans form, was detected in a discharged jet of a 1,3-diiode-but-2-ene (either in Z- or E-conformation) and O2 mixture diluted in Ar. Thirty pure rotational transitions with internal rotation splitting of the methyl top were observed. The observed frequencies were analyzed by the XIAM program, yielding an internal rotation barrier of 702.8(28) cm-1, which reasonably agrees with a theoretical value of 680 cm-1 determined with CCSD(T)/cc-pVTZ.
TL;DR: Silica gel-mediated Michael addition of 1,3-dicarbonyl compounds to methyl vinyl ketone and EVK was carried out to give the corresponding adducts in quite excellent yields as mentioned in this paper.
TL;DR: In this paper, the authors used a flow-through chamber method to determine the exchange rates of Methacrolein (MACR) and methyl vinyl ketone (MVK) in the presence of plant stomata.
Abstract: Methacrolein (MACR) and methyl vinyl ketone (MVK) are key intermediate compounds in isoprene-initiated reactions, and they cause the formation of secondary organic aerosols and photochemical ozone. The importance of higher plants as a sink of these compounds and as a source of volatiles converted from these compounds was addressed in the present study. We exposed four non-isoprene-emitting plant species to MACR and MVK at concentrations of several to several hundred ppb, measured their uptake rates, and analyzed the volatiles converted from MACR and MVK by these plants. We used a flow-through chamber method to determine the exchange rates. Both MACR and MVK were absorbed by all plants via stomata. Two metabolites, methyl ethyl ketone (MEK) and 2-butanol, were detected when MVK was fumigated. The conversion ratio was 26–39% for MEK and 33–44% for all volatiles. Combined with the results of two previous relevant reports, our results suggest that MEK conversion from MVK normally occurs in a wide range of plant species, but the conversion ratio may depend on plant type, i.e., if plant species are isoprene-emitting or non-emitting, as well as on the fumigation concentrations. This finding also emphasizes the importance of bilateral exchange measurements of these compounds at lower concentrations close to ambient levels.
TL;DR: In this article, a molecular beam of methyl vinyl ketone with a rotational temperature of 1.2(2) K was used to demonstrate the spatial separation of s-cis and s-trans conformers of the compound using the electrostatic deflector.
Abstract: Methyl vinyl ketone (C4H6O) is a volatile, labile organic compound of importance in atmospheric chemistry. We prepared a molecular beam of methyl vinyl ketone with a rotational temperature of 1.2(2) K and demonstrated the spatial separation of the s-cis and s-trans conformers of methyl vinyl ketone using the electrostatic deflector. The resulting sample density was 1.5(2) × 108 cm-3 for the direct beam in the laser ionization region. These conformer-selected methyl vinyl ketone samples are well suited for conformer-specific chemical reactivity studies such as in Diels-Alder cycloaddition reactions.
01 Feb 2020
TL;DR: In this paper, the bimolecular reactions of methyl vinyl ketone oxide (MVK-OO) with H2O, H2S, NH3, their dimer forms, and CH3NH2, have been studied.
Abstract: The bimolecular reactions of methyl vinyl ketone oxide (MVK-OO) with H2O, H2S, NH3, their dimer forms, and CH3NH2, have been studied. The reactions of (H2O)2 and (NH3)2 exhibit an effect of reducing the free energies of activation (ΔG‡); a catalytic behavior. The former energy barriers decrease by 20 kJ mol−1 while the latter by 14 kJ mol−1. In contrast, additional molecules in H2S reactions increase the calculated ΔG‡ values by 22 kJ mol−1. The calculations of MVK-OO + CH3NH2 predict ΔG‡ = 26 kJ mol−1, lower than the catalyzed reactions of H2O, H2S, and NH3. Additional molecules in CH3NH2 reactions lead to negligible effects on the energy, except for the (CH3NH2⋯H2O) reaction, where ΔG‡ is reduced by 10 kJ mol−1. The formation of a carbonyl hydroperoxide (via MVK-OO + HCO2H) is predicted to be the least favorable pathway with ΔG‡ values in the range of 61–69 kJ mol−1.
TL;DR: An optimized procedure for Wieland-Miescher Ketone synthesis using crude lipase preparations is created, characterizing both reaction yield and enantiomeric excess and proposing a general absorbance-based screening methodology for assessing biocatalytic potential of crude enzyme preparations for synthesis of WMK.
Abstract: Lipases, a versatile class of biocatalysts, have been shown to function in non-aqueous media/organic solvents and to possess “promiscuous” catalytic activity for a wide range of organic transformations. In this study, we explored the biocatalytic properties of a library of commercially available lipases by screening them for catalysis of a one-pot synthesis of Wieland–Miescher ketone, an important intermediate in the synthesis of biologically active compounds such as steroids and terpenoids, from methyl vinyl ketone and 2-methyl-1,3-cyclohexanedione. As a direct outgrowth of this screen, we created an optimized procedure for Wieland–Miescher ketone (WMK) synthesis using crude lipase preparations, characterizing both reaction yield and enantiomeric excess. We also identified principal components of the crude lipase mixture through proteomics and present evidence for a non-lipolytic origin of the observed catalysis. Finally, using the optimized conditions developed in this study, we propose a general absorbance-based screening methodology for assessing biocatalytic potential of crude enzyme preparations for synthesis of WMK.
TL;DR: In this article, the electronic structure calculation at the multi-configurational CASSCF and multi-state MS-CASPT2 levels, as well as the trajectory surface-hopping nonadiabatic dynamics simulation was carried out to reveal the different fates of syn/anti configurations in photochemical process.
Abstract: Methyl vinyl ketone oxide, an unsaturated four-carbon Criegee intermediate produced from the ozonolysis of isoprene has been recognized to play a key role in determining the tropospheric OH concentration. It exists in four configurations (anti-anti, anti-syn, syn-anti, and syn-syn) due to two different substituents of saturated methyl and unsaturated vinyl groups. In this study, we have carried out the electronic structure calculation at the multi-configurational CASSCF and multi-state MS-CASPT2 levels, as well as the trajectory surface-hopping nonadiabatic dynamics simulation at the CASSCF level to reveal the different fates of syn/anti configurations in photochemical process. Our results show that the dominant channel for the S1-state decay is a ring closure, isomerization to dioxirane, during which, the syn(C-O) configuration with an intramolecular hydrogen bond shows slower nonadiabatic photoisomerization. More importantly, it has been found for the first time in photochemistry of Criegee intermediate that the cooperation of two heavy groups (methyl and vinyl) leads to an evident pyramidalization of C3 atom in methyl-vinyl Criegee intermediate, which then results in two structurally-independent minimal-energy crossing points (CIs) towards the syn(C-O) and anti(C-O) sides, respectively. The preference of surface hopping for a certain CI is responsible for the different dynamics of each configuration.
TL;DR: Observed spectra can provide valuable information for the understanding of the mechanism of formation of Criegee intermediate MVKO from the source reaction of photolysis of (CH2I)HC=C(CH3)I in O2 in the laboratory.
Abstract: Ozonolysis of isoprene to produce Criegee intermediates such as methyl vinyl ketone oxide (MVKO), C2H3C(CH3)OO, is an important process in atmospheric chemistry MVKO was recently produced and iden
TL;DR: In this paper, the authors reported on the catalytic dehydration of 3-hydroxybutanone to butenone (but-3-en-2-one or methyl vinyl ketone), which could become a key step in a new bio-based process for the production of vitamin A.
Dissertation•
07 Dec 2020
TL;DR: In this article, the catalytic potential of a library of commercially available lipases was investigated by screening them for catalysis of the Robinson Annulation, a synthetically important carbon-carbon bond forming reaction.
Abstract: Biocatalysts derived from biological molecules such as proteins, RNA, and DNA have long been exploited for applications in synthetic chemistry. Lipases, a versatile class of biocatalysts, are known to exhibit significant promiscuity for non-native substrates in non-aqueous and mixed organic/aqueous solvents. While lipases are known to possess catalytic activity for a wide range of organic transformations, predicting which lipases will catalyze specific carbon-carbon bond forming reactions remains a significant challenge. In this study, the catalytic potential of a library of commercially available lipases was investigated by screening them for catalysis of the Robinson Annulation, a synthetically important carbon-carbon bond forming reaction. Specifically, the lipase library was screened for synthesis of the Wieland-Miescher Ketone, an important intermediate in the synthesis of biologically active compounds such as steroids and terpenoids, from methyl vinyl ketone and 2-methyl-1,3-cyclohexanedione. An optimized procedure is presented for Wieland-Miescher Ketone synthesis using a crude preparation of porcine pancreatic lipase (PPL), reporting on both yield and enantiomeric excess. Finally, commercially available lipases are often sold as crude preparations, containing many different proteins, and are often used by many researchers without further purification, potentially obscuring the identity of the catalytic species. Therefore, a methodology to isolate and characterize the active component(s) of these lipase formulations is described in this study.